1. Field of the Invention
The present invention generally relates to a low profile board-to-board connector assembly, and more particularly to a connector assembly having a receptacle and a plug which is capable of assuring a reliable electrical contact therebetween.
2. The Related Art
The trend of the electronic industry is to constantly reduce the size of electronic devices. Board-to-board connectors to electrically connect parallel printed circuit boards in the electronic devices are correspondingly required tinier and tinier. Moreover, contacts of the connectors are arranged thicker and thicker. These changes make high precision requirements of the connectors, and it is desirable to assure the reliable electrical contact between contacts of the receptacle and the plug.
U.S. Pat. Nos. 5,931,689, 5,842,875, 5,836,773, 5,830,018, 5,639,248, 5,626,500, 5,626,482, 5,599,192 and 5,161,985 disclose a traditional board-to-board connector assembly composed of a receptacle with a plurality of first contacts and a plug with a plurality of second contacts. Each of the first contacts has a S-shaped or U-shaped portion to provide a first spring contact end at its free end. While, each of the second contacts is shaped to have a straight contact end for pressed contact with the first spring contact end. The normal force to achieve the pressed contact only comes from a resilient deformation of the first spring contact end. In order to maintain a reliable contact between the contacts, it is necessary to make the S-shaped or U-shaped portion develop a considerably large spring bias. In this consequence, however, it becomes difficult to insert or remove the plug into and from the receptacle. Otherwise, poor electrical contact would result. Further, the straight contact end of the second contact is required to be held to a plug housing over a long length so as to be firmly fixed thereto, thereby an extra height is added to the plug and the assembly, which hinders the assembly from achieving a low profile design.
U.S. Pat. No. 5,520,545 discloses another traditional board-to-board connector assembly. First and second contacts of the assembly each have a U-shaped spring portion. The first and the second U-shaped spring portions are oriented in opposite directions in the assembled condition. However, such configuration cannot permit to give a contact point at the interface between the free ends of the spring contact ends. With this result, substantially only one of the U-shaped portions is best utilized to give a spring bias for providing a contact pressure between the first and the second spring contacts. Therefore, adequate contact pressure for reliable electrical connection between the first and the second contacts still cannot be achieved. If the contact area of the first and the second contacts is increased to solve above problem, it is also a hindrance to minimize the assembly.
U.S. Pat. No. 5,975,916 discloses another traditional board-to-board connector assembly. Each of first contacts of the assembly has a S-shaped portion composed of inverted and upright U-shaped portions. Each of second contacts of the assembly has a U-shaped portion. In the assembled condition, upright U-shaped portion of the first contact and U-shaped portion of the second contact are oriented in the same direction. With this structure, however, stress tends to concentrate on a bottom of the upright U-shaped portion where has a risk of occurring fatigue, and reliable electrical contact within the assembly cannot be assured.
An object of the present invention is to provide a low profile board-to-board connector assembly which is designed so as to provide a sufficient contacting pressure for reliable electrical contact within the assembly.
The low profile board-to-board connector assembly in accordance with the present invention comprises a receptacle and a detachable plug. The receptacle has a receptacle housing with a plurality of arrayed first contacts mounted therein. Each first contact has a base portion, a first solder tail portion extending outwardly from one end of the base portion for connection with a first printed circuit board (PCB), a retention portion perpendicular to the base portion, and a free first spring contact portion bent from the other end of the base portion and extending parallel to the retention portion. The plug has a plug housing with a plurality of arrayed second contacts mounted therein. Each second contact has a U-shaped portion with a pair of legs one of which is a free second spring contact portion and the other of which is a locking portion, and a second solder tail potion bent from an end of the locking portion and extending outwardly for connection with a second PCB. When the receptacle and the plug are assembled, the first spring contact portion can engage at its free end with the free end of the second spring contact portion thereby providing sufficient spring bias for reliable electrical contact with each other.